We construct static and spherically symmetric black hole solutions in the
Einstein-Euler-Heisenberg (EEH) system which is considered as an effective
action of a superstring theory. We considered electrically charged,
magnetically charged and dyon solutions. We can solve analytically for the
magnetically charged case. We find that they have some remarkable properties
about causality and black hole thermodynamics depending on the coupling
constant of the EH theory $a$ and $b$, though they have central singularity as
in the Schwarzschild black hole.Comment: 8 pages, 13 figures, figures corrected and some comments adde